A mechanical chopper is designed based on the programmable logic controller, servo motor amplifier, servo motor and encoder. The interaction potential measurement system is constructed by the mechanical chopper and dual optical tweezers. The characteristic of the system such as the design of the chopper, the switching time of the blinking optical tweezers, the tuning range, the origin position return feature, the compatibility and the usability of the system are discussed. The system is used to measure the interaction potential of a pair polystyrene spheres. The result is consistent with the Darjaguin-Landau-Verwey-Overbeek theory, which demonstrates the reliability of the apparatus. In addition, the apparatus provides an effective technique for measuring the interaction potential between two micro colloidal particles.